Microvalve having magnetic wax plug and flux control method using magnetic wax

ABSTRACT

Provided is a microvalve having a magnetic wax plug which includes a micro fluidic structure having an inlet portion and an outlet portion, a magnetic wax plug provided at a predetermined section where the inlet portion and the outlet portion meet, existing in a solid state, melted at a temperature higher than a predetermined temperature, and reversibly moving along a magnetic field, so as to control flux of a fluid through the micro fluidic structure, a heating portion provided corresponding to the section and heating the magnetic wax plug to be melted, and a magnetic field application portion selectively applying a magnetic field to a position where the melted magnetic wax plug arrives.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2005-0027829, filed on Apr. 2, 2005, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microvalve and a microchip having amicro fluidic structure, and more particularly, to a bi-stable and phasechange type microvalve provided in a micro fluidic structure and amicrochip including the microvalve.

2. Description of the Related Art

In general, a valve refers to an apparatus that is connected to a pipeto control the amount of flow or pressure of a fluid. A microvalve andother apparatuses comprising a microvalve related to a micro fluidicstructure have received wide attention, particularly in a bio-chemicalfield including a micro total analysis system (μTAS). The microvalve iswidely used not only in the μTAS related to the development of newmedicines, a clinical diagnosis system, and a biomedical research fieldsuch as a DNA, but also in an inkjet print field.

The microvalve developed with the development of amicro-electromechanical system (MEMS), or a so-called MEMS valve, has aimportant role in the micro fluidic structure with a micropump, as animportant device having functions of allowing, limiting, and blockingthe flow of a fluid including gas or liquid. The microvalvesmanufactured using a fine processing technology have a variety ofstructures and sizes from several micrometers to about 1 mm according tothe type of driving and purpose.

A phase change valve has been studied among the various types ofmicrovalves. The phase change valve refers to a tangible valve that isincluded in the micro fluidic structure to exist in a solid state andcontrols the flow of a fluid in a mode. The state of the phase changevalve is changed from the solid state to a liquid state, causing adisplacement or deformation, when the mode is changed to another mode.U.S. Pat. No. 6,679,279 and U.S. Patent Publication No. 2004-0219732disclose the above phase change valve. A conventional phase change valveis described below with reference to FIGS. 1A, 1B, 2A, and 2B.

FIGS. 1A and 1B show an example of the conventional phase change valve,in which FIG. 1A shows a closed mode in which a channel is closed andFIG. 1B shows an open mode in which the channel is open. Referring toFIGS. 1A and 1B, a microchannel 21 is formed in a substrate 20. A well22 is formed at a side of the channel 21. A solid wax plug 40 isprovided in the microchannel 21 at the upper stream thereof with respectto the well 22. A solid wax is a material which exists in a solid stateat the room temperature and its fluidity grows as it is heated. Atypical material for the solid wax is paraffin wax.

A heating portion 30 capable of selectively radiating heat is providedaround the solid wax plug 40. When the heating portion 30 radiates heatin the state as shown in FIG. 1A, the solid wax plug 40 is melt. A meltwax 40′ flows into the well 22 by the pressure of a fluid flowing in themicrochannel 21 and becomes solid in the well 22. However, since themode change of the conventional phase change valve 101 is irreversible,once the valve opens, the valve cannot be reused.

FIGS. 2A and 2B show another example of the conventional phase changevalve. Referring to FIGS. 2A and 2B, a phase change valve 102 has a Yshaped connection portion where an inlet portion 23, an outlet portion24, and a vent portion 25 meet. A heating portion 30 is provided aportion extending from the Y shaped connection portion to the ventportion 25. As shown in FIG. 2A, when the valve 102 is in an open mode,a solid wax plug 42 is located in the Y shaped connection portion. Whenthe valve 102 is in a closed mode as shown in FIG. 2B, the solid waxplug 42 is moved to the vent portion 25.

For mode change, the solid wax plug 42 is melt using the heating portion30 and a melted wax is moved by an air pressure and vacuum chamber (orpump) that is selectively connected to a side of the vent portion 25.Thus, this type of the valve 102 needs a connection to a high pressureor vacuum chamber (or pump) using another valve for the driving of thevalve. To facilitate miniaturization of the valves in units ofmicrometers and provide a micro fluidic structure which can be reused,the above disadvantages that the conventional phase change valves 101and 102 have must be overcome.

SUMMARY OF THE INVENTION

To solve the above and/or other problems, the present invention providesa microvalve which requires the minimum number of additional parts forvalve driving microvalve and can be reused by a reversible mode change.

The present invention provides a microchip having a micro fluidicstructure to which the microvalve is applied.

According to an aspect of the present invention, a microvalve having amagnetic wax plug comprises a micro fluidic structure having an inletportion and an outlet portion, a magnetic wax plug provided at apredetermined section where the inlet portion and the outlet portionmeet, existing in a solid state, melted at a temperature higher than apredetermined temperature, and reversibly moving along a magnetic field,so as to control flux of a fluid through the micro fluidic structure, aheating portion provided corresponding to the section and heating themagnetic wax plug to be melted, and a magnetic field application portionselectively applying a magnetic field to a position where the meltedmagnetic wax plug arrives.

According to another aspect of the present invention, a microchip usinga magnetic wax which performs a chemical reaction test with a smallamount of a liquid test material using a micro fluidic structure formedon a substrate comprises a micro fluidic structure having a fine channelthrough which the liquid test material passes, and a magnetic wax memberprovided at a predetermined section of the micro fluidic structure,existing in a solid state, melted at a temperature higher than apredetermined temperature, and reversibly moving along a magnetic field,so as to control flux of a fluid through the micro fluidic structure.

According to another aspect of the present invention, a microchip unitusing a magnetic wax including a microchip which performs a chemicalreaction test with a small amount of a liquid test material using amicro fluidic structure formed on a substrate and a driving apparatusportion accommodating and driving the microchip comprises a microfluidic structure having a fine channel through which the liquid testmaterial passes, and a magnetic wax member provided at a predeterminedsection of the micro fluidic structure, existing in a solid state,melted at a temperature higher than a predetermined temperature, andreversibly moving along a magnetic field, so as to control flux of afluid through the micro fluidic structure, wherein the driving apparatusportion comprises a heating portion provided to correspond to apredetermined section of the micro fluidic structure and radiating heatto melt the magnetic wax member, and a magnetic field applicationportion selectively applying a magnetic field to a position where themelted magnetic wax member arrives.

According to another aspect of the present invention, a method forcontrolling flux of a fluid in a micro fluidic structure by applyingheat to a solid wax in the micro fluidic structure to move in a meltedstate comprises preparing a magnetic wax formed of a homogenous mixtureof a ferrofluid and the solid wax and arranging the magnetic wax in apredetermined section of the micro fluidic structure, and controllingflux of the fluid by melting the magnetic wax by applying heat to thesection and moving the magnetic wax by applying a magnetic field to aposition where the melted magnetic wax arrives.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawings in which:

FIGS. 1A and 1B show an example of the conventional phase change valve;

FIGS. 2A and 2B show another example of the conventional phase changevalve;

FIG. 3 shows a microchip having a microvalve according to an embodimentof the present invention;

FIG. 4 shows the microvalve according to an embodiment of the presentinvention;

FIGS. 5A through 5F show the operation of the microvalve of FIG. 4;

FIG. 6 shows a modification of the microvalve of FIG. 4;

FIG. 7 shows a microvalve according to another embodiment of the presentinvention;

FIG. 8 shows the construction of a system for testing the performance ofa microvalve; and

FIG. 9 is a graph showing a melting temperature according to thecomposition of a magnetic wax.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the accompanying drawings, the same reference numeralsindicate the same elements having the same functions. FIG. 3 shows amicrochip having a microvalve according to an embodiment of the presentinvention. Referring to FIG. 3, a microchip 110 has a predeterminedmicro fluidic structure formed in a substrate 200. The micro fluidicstructure includes a plurality of microchannels and a microchamber 230.The microchannels include an inlet portion 210 having a test materialinput hole 211 at an end thereof, an outlet portion 220 connected to themicrochamber 230, and a vent portion 250 which are connected together bya Y shaped or T-shaped connection portion. A magnetic wax member 500 isprovided in the Y-shaped connection portion. A heating portion 300capable of melting the magnetic wax member 500 by radiating heat isprovided around the Y-shaped connection portion. The microchip 110 canbe provided by itself or as a microchip unit including the microchipwith a driving apparatus portion (not shown) for driving the microchip110.

The micro fluidic structure is a structure in which at least onedimension has a size of several or several hundreds of micrometers andincludes a channel, a chamber, a pipe, or a combination thereof throughwhich a fluid such as gas or liquid can flow. The micro fluidicstructure can include an actuator such as a valve or pump. As an exampleof the micro fluidic structure, the inlet portion 210, the outletportion 220, and the vent portion 250 are connected at a point by aY-shaped or Y-shaped connection portion, as shown in FIG. 3. Inaddition, a variety of shapes are available for the connection portion.

The magnetic wax is a homogenous mixture of a ferrofluid and a solid waxwhich exits in a solid state at the room temperature and in a liquidstate at a high temperature, exhibiting fluidity, and a material thathas a magnetism and flows along a magnetic filed. The ferrofluidincludes a magnetic particle exhibiting a ferromagnetic property, asurfactant enclosing the surface of the magnetic particle, and acarrier. The carrier is formed of a hydrocarbon based material for thehomogenous mixture with common solid wax. The solid wax, as ahydrocarbon based material, exits in a solid state at the roomtemperature and has a fluidity at a high temperature. A common paraffinwax is used as the solid wax. The property of the magnetic wax formed bymixing a ferrofluid and paraffin wax is briefly described as aparaffin-based ferrofluid in a document entitled “Ferrofluid andNanoparticle Applications to Nanotechnology” (Markus Zahn, Journal ofNanoparticle Research, vol 3, pp. 73-78, 2001).

The heating portion 300 may be a resistance heating unit installed onthe substrate 200 and radiating heat by receiving electrical energy fromthe outside. Alternatively, the heating portion 300 can be installed atthe driving apparatus portion accommodating and driving the microchip110 to transfer heat around the magnetic wax member 500.

The magnetic wax member 500 melted by the heating portion 300 is movedby a magnetic field applied at a selected position by a magnetic fieldapplication portion (not shown). The magnetic wax member 500 that ismelted and moved is cooled and solidified again, forming a new mode, sothat the flux in the micro fluidic structure is controlled.

The magnetic field application portion may be a solenoid portionselectively acting to at least two positions of the microchip 110. Inthis case, the solenoid portions can be installed on the microchip 110itself or on the driving apparatus portion which accommodates and drivesthe microchip 110. Also, the magnetic field application portion may beat least one permanent magnet affecting the magnetic wax member 500while moving outside the microchip 110. The permanent magnet can beinstalled on the driving apparatus portion capable of moving.

FIG. 4 shows the microvalve according to an embodiment of the presentinvention. Referring to FIG. 4, a microvalve 112 includes a Y-shapedconnection portion where an inlet portion 210, an outlet portion 220,and a vent portion 250 meet at one point. The magnetic wax member 500 isselectively located in the Y-shaped connection portion or the ventportion 250. The heating portion 300 which can melt the magnetic waxmember 500 is provided around the Y-shaped portion. The heating portion300 has a switch (not shown) so as to be selectively radiate heat onlywhen the mode of the microvalve 112 changes.

Also, the microvalve 112 includes magnetic field application portions401 and 401′ which selectively apply a magnetic field to the Y-shapedconnection portion and the vent portion 250 to move the magnetic waxmember 500 that is melted. The magnetic field application portion may bea permanent magnet which can move between two positions or a solenoidportion located at each of the two positions and selectively applying amagnetic field.

With the following description on the operation of the microvalveaccording to the present invention, the characteristic features of themicrovalve and a flux control method using a magnetic wax are describedin detail. FIGS. 5A through 5F show the operation of the microvalve ofFIG. 4. The microvalve 112 according to the above embodiment has aclosed mode for blocking the flux through the inlet portion 210 and theoutlet portion 220 and an open mode for allowing the flux.

FIG. 5A shows the closed mode. In FIG. 5A, a magnetic wax plug 501 in asolid state at the room temperature clogs the center of the Y-shapedconnection portion. FIGS. 5B through 5D show the process of conversionfrom the closed mode to the open mode. Referring to FIG. 5B, themagnetic field application portion 401′ is located at the vent portion250. Next, as shown in FIG. 5C, the heating portion 300 is operated toheat the magnetic wax plug 501. A melted magnetic wax 501′ having afluidity is moved toward the vent portion 250 by the magnetic fieldapplication portion 401′. The operation of the heating body 300 isstopped and the melted magnetic wax 501′ is cooled as shown in FIG. 5Fand located in the vent portion 250. Thus, the open mode is formed andthe flux between the inlet portion 210 and the outlet mode 220 isallowed.

FIG. 5E through 5F show the process of converting the open mode to theclosed mode. As shown in FIG. 5E, the magnetic field application portion401 is located at the central portion of the Y-shaped connectionportion. As shown in FIG. 5F, the heating portion 300 is operated tomelt the magnetic wax plug 501′ of FIG. 5E. A melted magnetic wax 502′is moved toward the Y-shaped connection portion by the magnetic fieldapplication portion 401. Next, the operation of the heating portion 300is stopped and the melted magnetic wax 502′ is cooled so that the modeis changed to the closed mode shown in FIG. 5A.

It is preferred that the application of the magnetic field by themagnetic field application portion precede in time the melting of themagnetic wax plug to prevent the unnecessary flux of the melted magneticwax. However, the present invention is not limited thereto so that theapplication of the magnetic field and the melting of the magnetic waxplug can be performed in the reverse order or at the same time.

FIG. 6 shows a modification of the microvalve of FIG. 4. Referring toFIG. 6, the inlet portion 210, the outlet portion 220, and the ventportion 250 constitute the micro fluidic structure and a solid wax plug42 is provided in the micro fluidic structure. The heating portion 300is provided to melt the solid wax plug 42. A ferrofluid 450 is injectedinto the vent portion 250 to be close to the solid wax plug 42. Amagnetic field application portion 400 is provided to move theferrofluid 450. When the solid wax plug 42 is melted, the ferrofluid 450is moved so that the position of the solid wax plug 42 is changed.

FIG. 7 shows a microvalve according to another embodiment of the presentinvention. Referring to FIG. 7, a microvalve according to the presentembodiment includes an inlet portion 230 and an outlet portion 240 whichare arranged linearly and a well portion 232 formed on a lower surfaceof a portion where the inlet portion 230 and the outlet portion 240 meetto be inclined with respect to the inlet portion 230. In the closedmode, a magnetic wax plug 500 is located in the inlet portion 230 at theupper stream of a channel with respect to the well portion 232.

When the mode is changed to the open mode, the heating portion 300 isoperated to melt the magnetic wax plug 500. Then, the melted magneticwax is moved along an inclined surface and contained in the well portion232 so that the flux between the inlet portion 230 and the outletportion 240 is allowed. In contrast, when the open mode is changed tothe closed mode, a magnetic field is applied so that the melted magneticwax is moved along the inclined surface toward the upper stream.

FIG. 8 shows the construction of a system for testing the performance ofa microvalve. An allowable pressure is measured using the system shownin FIG. 8 when the microvalve according to the present invention is inthe closed mode. A ferrofluid and paraffin wax are mixed in a volumeratio of 1:2. “APG E18, 138 Gauss” by a U.S. company, Ferrotech, and“76232, sp 68-74° C.” by a U.S. company, Fluka, are used for theferrofluid and the paraffin wax, respectively. The volume of themagnetic wax plug is 0.2 μl. It is noted that the maximum allowablepressure of the microvalve according to the first embodiment reachesabout 50 Psi.

FIG. 9 is a graph showing a melting temperature according to thecomposition of a magnetic wax. A change of optical characteristicaccording to a change in temperature is measured for a pure paraffin waxand a magnetic wax having the same composition as the magnetic wax plugused in the above test to compare melting temperatures between the twowaxes. The phase change of the magnetic wax occurs in a hatched area inthe graph of FIG. 9. However, the phase change temperature of themagnetic wax is not limited to the hatched area in the graph and canvary according to the type of a mixed solid wax. By using this feature,magnetic waxes having various phase change temperatures according to thetype and temperature condition of fluid of which flux is to becontrolled can be provided.

In a method of controlling the flux of fluid using a magnetic waxaccording to the present invention, a magnetic wax is arranged in apredetermined section in the micro fluidic structure. The magnetic waxis made by homogeneously mixing a ferrofluid with a solid wax. Thearrangement of the magnetic wax can be performed during themanufacturing process of a microvalve or a microchip according to thepresent invention.

To control the flux in the micro fluidic structure, heat is applied tothe section in the micro fluidic structure to melt the magnetic wax anda magnetic field is applied to a position where the melted magnetic waxis supposed to arrive so that the magnetic wax is moved. The order ofthe application of the magnetic field and the melting of the magneticwax plug is not fixed so that any of both steps can be performed firstor both steps can be performed at the same time.

As described above, in the microvalve, the microchip, the microchipunit, and the flux control method according to the present invention,the structure required for the control of fine flux is simplified andthe apparatus can be reused through a reversible mode change.

The microvalve having a magnetic wax plug according to the presentinvention including the micro fluidic structure can be applied to avariety of fields performing any kind of job by controlling the flux ofgas or liquid in the micro fluidic structure. In particular, the presentinvention can be applied to a lab-on-a-chip in which a variety ofconstituent elements of a biological or biochemical laboratory arefinely classified and represented on a single chip and contribute to thedevelopments of DNA extraction, amplification, and detection techniques,cell separation and destruction test techniques, a cell virulence testtechnique, an HCS (high contents screening) technique, and a singlemolecule detection technique. Also, the microchip using the magnetic waxmember according to the present invention, the microchip unit, and theflux control method can be used not only for the microvalve, but alsofor an actuator such as a micropump.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A microvalve having a magnetic wax plug, the microvalve comprising: amicro fluidic structure having an inlet portion and an outlet portion; amagnetic wax plug provided at a predetermined section where the inletportion and the outlet portion meet, existing in a solid state, meltedat a temperature higher than a predetermined temperature, and reversiblymoving along a magnetic field, so as to control flux of a fluid throughthe micro fluidic structure; a heating portion provided corresponding tothe section and heating the magnetic wax plug to be melted; and amagnetic field application portion selectively applying a magnetic fieldto a position where the melted magnetic wax plug arrives.
 2. Themicrovalve as claimed in claim 1, wherein the micro fluidic structurecomprises a Y-shaped connection portion which connects the inletportion, the outlet portion, and a vent portion, and the magnetic waxplug is selectively located at the vent portion and the Y-shapedconnection portion to allow or restrict flux of a fluid through theinlet portion and the outlet portion according to the location of themagnetic wax plug.
 3. The microvalve as claimed in claim 1, wherein themicro fluidic structure further comprises a well portion provided in alower portion of a position where the inlet portion and the outletportion meet, inclined downward from the inlet portion toward the outletportion, and the magnetic wax plug is selectively located at the inletportion and the well portion to allow or restrict flux of a fluidthrough the inlet portion and the outlet portion according to thelocation of the magnetic wax plug.
 4. The microvalve as claimed in claim1, wherein the magnetic wax plug is formed of a mixture of ferrofluidand paraffin wax.
 5. The microvalve as claimed in claim 1, wherein theferrofluid is based on hydrocarbon.
 6. The microvalve as claimed inclaim 1, wherein the magnetic field application portion is a movablepermanent magnet.
 7. The microvalve as claimed in claim 1, wherein themagnetic wax plug selectively moves to at least two positions in amelting state, and the magnetic field application portion is a solenoidportion which is provided at at least two positions and selectivelyoperated.
 8. A microchip using a magnetic wax which performs a chemicalreaction test with a small amount of a liquid test material using amicro fluidic structure formed on a substrate, the microchip comprising:a micro fluidic structure having a fine channel through which the liquidtest material passes; and a magnetic wax member provided at apredetermined section of the micro fluidic structure, existing in asolid state, melted at a temperature higher than a predeterminedtemperature, and reversibly moving along a magnetic field, so as tocontrol flux of a fluid through the micro fluidic structure.
 9. Themicrochip as claimed in claim 8, further comprising a heating portionprovided in a predetermined section of the micro fluidic structure andheating the magnetic wax member at a temperature higher than thepredetermined temperature.
 10. The microchip as claimed in claim 8,further comprising a solenoid portion provided at each of at least twopositions to which the magnetic wax member selectively moves in a meltedstate.
 11. The microchip as claimed in claim 8, wherein the microfluidic structure comprises a Y-shaped connection portion which connectsan inlet portion, an outlet portion, and a vent portion, and themagnetic wax member is selectively located at the vent portion and theY-shaped connection portion to allow or restrict flux of a liquid testmaterial through the inlet portion and the outlet portion according tothe location of the magnetic wax member.
 12. The microchip as claimed inclaim 8, wherein the micro fluidic structure comprises an inlet portion,an outlet portion, and a well portion provided in a lower portion of aposition where the inlet portion and the outlet portion meet, inclineddownward from the inlet portion toward the outlet portion, and themagnetic wax member is selectively located at the inlet portion and thewell portion to allow or restrict flux of a liquid test material throughthe inlet portion and the outlet portion according to the location ofthe magnetic wax member.
 13. The microchip as claimed in claim 8,wherein the magnetic wax member is formed of a mixture of ferrofluid andparaffin wax.
 14. The microchip as claimed in claim 13, wherein theferrofluid is based on hydrocarbon.
 15. A microchip unit using amagnetic wax including a microchip which performs a chemical reactiontest with a small amount of a liquid test material using a micro fluidicstructure formed on a substrate and a driving apparatus portionaccommodating and driving the microchip, the microchip chip comprising:a micro fluidic structure having a fine channel through which the liquidtest material passes; and a magnetic wax member provided at apredetermined section of the micro fluidic structure, existing in asolid state, melted at a temperature higher than a predeterminedtemperature, and reversibly moving along a magnetic field, so as tocontrol flux of a fluid through the micro fluidic structure, wherein thedriving apparatus portion comprises: a heating portion provided tocorrespond to a predetermined section of the micro fluidic structure andradiating heat to melt the magnetic wax member; and a magnetic fieldapplication portion selectively applying a magnetic field to a positionwhere the melted magnetic wax member arrives.
 16. The microchip unit asclaimed in claim 15, wherein the magnetic wax member selectively movesto at least two positions in a melting state, and the magnetic fieldapplication portion is a solenoid portion which is provided at at leasttwo positions and selectively operated.
 17. The microchip unit asclaimed in claim 15, wherein the micro fluidic structure comprises aY-shaped connection portion which connects an inlet portion, an outletportion, and a vent portion, and the magnetic wax member is selectivelylocated at the vent portion and the Y-shaped connection portion to allowor restrict flux of a liquid test material through the inlet portion andthe outlet portion according to the location of the magnetic wax member.18. The microchip unit as claimed in claim 15, wherein the micro fluidicstructure comprises an inlet portion, an outlet portion, and a wellportion provided in a lower portion of a position where the inletportion and the outlet portion meet, inclined downward from the inletportion toward the outlet portion, and the magnetic wax member isselectively located at the inlet portion and the well portion to allowor restrict flux of a liquid test material through the inlet portion andthe outlet portion according to the location of the magnetic wax member.19. The microchip unit as claimed in claim 15, wherein the magnetic waxmember is formed of a mixture of ferrofluid and paraffin wax.
 20. Themicrochip unit as claimed in claim 19, wherein the ferrofluid is basedon hydrocarbon.